Computer-to-plate (CTP) is an imaging technology used in printing processes, in which image data is output directly from a computer to a printing plate by exposing the printing plate to light energy according to the image data. A printing plate, such as a polymer plate covered by a thin ablatable layer is positioned on an imaging cylinder, e.g., the cylinder (also called drum) of an external drum imaging device. As the cylinder rotates around its axis, an image head moves in the axial direction and focuses one or more laser beams modulated with image data on to the plate's ablatable surface to ablate a pattern.
The process of positioning and aligning one or more printing plates on a cylinder is referred to as registration.
Pre-punched plates are used to allow accurate positioning and alignment on a cylinder. A pre-punched plate has registration holes, e.g., two holes punched near one edge of the plate that match register pins on the cylinder to secure alignment. Because the distance between two holes of a pre-punched plate varies depending on the width of the plate, there is a need to accommodate pairs of register pins that are spaced differently for different width plates.